NWS Rapid City, SD - The Rapid City Flood of 1972

The Rapid City Flood of 1972

36 Years After the Flood

Many technological advances have been made since the 1972 Rapid City Flood. In the 36 years since the flood, improvements in communications, technology and changes to zoning laws have helped create a safer community.

Rapid City National Weather Service Office as it looked in 1972.

In 1972, the primary duties of the National Weather Service Office (NWS) in Rapid City were taking twice-daily upper air observations, hourly surface observations, issuing local storm warnings and providing local forecasts to the media. Forecasts were made by the NWS offices in Sioux Falls, South Dakota and Minneapolis, Minnesota and flood warnings were issued by the NWS office in Sioux City, Iowa. The personnel in Rapid City were not trained to make forecasts and use new technologies and procedures to issue warnings; instead, they relied on reports of severe weather from people across the area. The staff at Rapid City also lacked access to vital weather data needed to issue warnings.

Rapid City National
Weather Service
Office, 2002.

The Rapid City National Weather Service Office is now a forecast office with a full-time staff of meteorologists who issue all the forecasts and warnings for northeastern Wyoming and the western third of South Dakota. In order to fully utilize the equipment available in the offices, forecasters and technicians frequently attend seminars and training sessions to improve their skills and learn new forecasting techniques. Staff members also research storm events in the local area to gain a better understanding of the effects of the Black Hills on the weather.

All National Weather Service offices are connected by a nationwide computer network called the Advanced Weather Information Processing System (AWIPS). Data from AWIPS is transmitted among the sites by telephone lines and satellite. Forecasters can examine weather observations, satellite images, radar data, lightning strike information, river observations and computer generated forecasts at their workstations. From these workstations, forecasters can select potential severe storms and have the computer compose the warning bulletin, including arrival time at locations along its path, and transmit it to other NWS offices, external users and NOAA Weather Radio.

National Weather Service Warnings

In 1972, the National Weather Service (NWS) Office in Rapid City did not have a teletype system to transmit warning bulletins to the media, emergency officials or other NWS offices. Instead, the NWS used a one-way hotline to the media to verbally notify them of warnings. Today, all NWS offices, including Rapid City, are connected by dedicated phone lines and satellite links that transmit data within the agency and to external users within seconds of issuance.

Warnings issued by the NWS are transmitted to a regional site where they are sent to the National Oceanic and Atmospheric Administration (NOAA) Weather Wire System satellite. Users, including the State Radio dispatch office in Pierre, receive the warnings through a satellite downlink, then retransmit them to local dispatchers. The warnings also enter the NWS's communications hub near Washington, DC and are relayed through news services to local media.

A local radio system allows NWS forecasters to communicate with the Rapid City-Pennington County Emergency Management office and the Pennington County Emergency Services Communications Center. The NWS will also join the new South Dakota state radio system this summer, allowing the staff to notify dispatches of warnings and to receive report of severe weather and flooding from law enforcement officials and weather spotters across the area.

NOAA Weather Radio

In the mid-1970's, the National Oceanic and Atmospheric Administration (NOAA), the NWS's parent organization, developed NOAA Weather Radio (NWR), a network of radio stations operated by local NWS offices. The continuous broadcasts provide current weather warnings, forecasts, and conditions and is the best method to receive severe weather warnings. The station serving Rapid City was installed in 1981, but broadcast at only 200 watts, so the range was quite limited. The power was eventually raised to 1,000 watts and coverage expanded to include the eastern slopes of the Black Hills.

Today, additional NWR stations on Terry Peak near Lead and Battle Mountain near Hot Springs provide almost complete coverage to the Black Hills and surrounding plains. Another station, located between Philip and Kadoka, serves the Badlands area. Three more stations will be installed near Porcupine, White River and Faith this summer, providing NWR coverage to nearly all of western South Dakota.

When forecasters issue warnings for tornadoes, severe thunderstorms, and flash floods; special receivers sound a tone which alert people even if they're sleeping, watching cable or satellite TV, don't live near a warning siren, are outdoors, or the electricity is off. People can also depend on it for valuable safety information about hazardous materials emergencies.

The special receivers needed to hear the broadcast and sound the tone alarm can be purchased at electronics, discount, sporting goods, hardware, department, drug, or office supply stores. You can also order them from catalogs specializing in outdoor equipment, weather-related items, or ranch and farm supplies.

The cost of a receiver ranges from $40 to $100. You should ensure the model you purchase has battery backup, tone alarm, and seven channel features (if you have an older model radio with three channels, you can't pick up the signals from the new stations). You may need an external antenna depending on the construction of your building or your location inside it or in some parts of the Black Hills. You may also want to consider a receiver that can be programmed to alert only for your county; this feature is called SAME for Specific Area Message Encoding. Some radios have an extra jack for a visual signal for hearing impaired people or use in a high-noise area.

Emergency Alert System

The Emergency Broadcast System (EBS) was designed to announce nuclear attack warnings over commercial radio and television through a "daisy chain" relay system. Stations would monitor one designated station in the area for emergency messages and manually activate the system. When someone at the primary station announced weather warnings, people at other stations listened for the warning signal, copied the information they heard and read it on their station. Other stations monitoring the secondary stations would repeat the process. If one station was off the air, the remainder of the stations never received the warnings.

The EBS was replaced by the Emergency Alert System (EAS) in 1997. All local radio and television stations as well as cable television systems monitor several other stations to ensure they receive emergency messages. The system can have warnings automatically interrupt routine broadcasts, even if no one is at the station. The EAS uses digital codes, so television stations can also scroll warning information as the message is announced. Stations can also monitor NWR signals for severe weather warnings. The Rapid City-Pennington County Emergency Management office can also activate the EAS from the Emergency Operations Center in the Pennington County Courthouse.

Sirens

In 1972, Rapid City had only four outdoor sirens. The county has installed nine additional sirens in the city since then and has four more serving outlying areas of the county.

Weather information is available from many more sources today than in 1972. The Internet has many sites with weather forecasts and warnings, including official National Weather Service products. Warning information is available through pager systems and small satellite systems are available for homes and businesses to provide warnings, forecasts and radar data.

Weather and Water Observations

In order to forecast conditions in the environment, it is necessary to obtain measurements of various elements. Instruments that record and transmit observations of temperature, precipitation, wind, humidity and river levels are scattered throughout the region.

Satellite

Satellite images are photographs of the earth taken from space and provide information for climate research, measurements of atmospheric temperature and humidity, monitoring of volcanic eruptions and global vegetation analysis. However, the use of satellite data to monitor storm development was not very advanced 36 years ago. Satellite images were available only during daylight hours, when the sun provided enough light to illuminate cloud features. The images were only available at a few NWS offices, but they did not have extra personnel to analyze and interpret the data.

Now, three types of satellite images are used in forecast operations. Visible images use reflected light, like a regular camera. Although this type of satellite provides very detailed images, the information is not available at night.

Infrared images are also available, rather than a visible image. Infrared energy radiated from the top of objects in the satellite's view creates these images, which are available 24 hours a day. Since atmospheric temperature decreases with height, clouds are cooler than ground temperatures and tall thunderstorms have even colder temperatures than regular clouds, they appear different in the images. Infrared images are often enhanced, or color-coded, to make features easier to distinguish.

Instead of taking a photograph or measuring infrared energy, the satellite detects the amount of water vapor in the air. It is an excellent tool to track larger scale storm systems and the path of jet streams, which affect the development of thunderstorms. These images are also available 24 hours a day. Water vapor images are also enhanced to make analysis easier.

Visible Satellite Image Infrared Satellite Image

Water Vapor Satellite Image

The Automated Surface
Observing System (ASOS).

Surface Observations

In 1972, hourly observations of temperature, dew point, wind speed and wind direction, sky condition, visibility, current weather and barometric pressure were taken by an observer. The information was recorded on a paper form as well as disseminated on a teletype machine.

Now, observations are obtained using Automated Surface Observing Systems (ASOS). When significant changes in current conditions occur, ASOS sends out a special observation. To augment the network of automated surface observations, volunteer observers provide daily temperature and precipitation data to the NWS. NWS meteorologists use surface observations to make forecast and warning decisions. The information is also input into forecast models to produce forecast guidance.

RADAR

Conventional radar

Doppler radar

The Rapid City Weather Service Office did not have its own radar in 1972, but could monitor a remote display from the radar at Ellsworth Air Force Base. However, the system was inoperable during the flood. The main NWS radar for South Dakota was located in Huron, but the Black Hills region was just beyond its range, so detailed information about the storms on June 9 was not included in the hourly reports issued by the radar observer. The NWS office in Rapid City also lacked a teletype machine, so the office didn't receive the reports. The South Dakota School of Mines and Technology (SDSM&T) Institute of Atmospheric Sciences also operated a radar and contacted the NWS Office periodically with information. However, the day of the flood, the radar was shut off at 7:00 p.m.

Radar, an acronym for "radio detection and ranging", was originally used by the military to track aircraft, but is now also an important observational tool for meteorologists. A weather radar unit sends out energy that bounces off objects in the atmosphere (such as precipitation) and returns part of the energy to a receiver. The returned signal is amplified and displayed on a screen for interpretation by meteorologists.

Upper Air Observations

The National Weather Service office in Rapid City is part of a network that takes observations of the upper atmosphere. Weather balloons carrying instruments called radiosondes are launched simultaneously at stations around the world. A radiosonde is an instrument that measures the temperature, pressure and humidity of the air. Analyzing data from the radiosonde also yields wind speed and direction information. Super computers collect, process and analyze observational data. Surface and upper air charts, based on the radiosonde data, provide forecasters with a three-dimensional view of the atmosphere.

River Gauge Network

Wire weight gauge

Data collection
platform, or DCP

To determine the stage, or how deep the water is at a given location, river gauges are used. Although there are many types of river gauges, they are classified as either recording or non recording. Two common types of non-recording gauges are staff gauges and wire weight gauges. A staff gauge is similar to a ruler, and the river level is read directly from the gauge.

A wire weight gauge consists of a drum wound with cable, a weight attached to the end of the cable, a graduated disc and a counter. When the bottom of the weight is resting on the water surface, a river stage reading can be obtained from the graduated disc and counter.

A limitation of non-recording gauges is the need for an observer. However, data collection platforms (DCP), are electronic devices connected to river or rain gauges to automatically record stage and precipitation data. In 1974, geosynchronous meteorological satellites were developed and launched by the National Aeronautics and Space Administration (NASA). Data collection platforms transmit data to meteorological satellites which in turn relay information to a remote computer for analysis.

Precipitation Network

Standard 8-inch
rain gauge.

Detail of a weighing rain gauge.

According to National Weather Service documents, the observational network in western South Dakota was about 50 percent complete at the time of the flood. Twenty sites in the area provided precipitation readings on a daily basis. Since 1972, the number of sites routinely reporting precipitation information has increased to 94.

Like river gauges, there are two types of precipitation gauges, recording and non-recording. The 8-inch standard non-recording rain gauge has been used since 1891 as the official precipitation measuring device. Rain, funneled into a narrower tube that "magnifies" the catch, can be read to the nearest hundredth of an inch using a specially calibrated measuring stick. The narrower tube holds up to 2 inches of rain, so the larger tube acts as an overflow.

Recording rain gauges not only measure the amount of rain, but the rate and which it falls. The Universal Weighing and Recording gauge collects rainfall in a weighing bucket. The weight of the precipitation in the bucket causes a pen to move and make a trace on a graph.

Other types of recording gauges include the Fischer and Porter punched tape recorder and the tipping bucket. Fischer and Porter gauges punch a paper to record the amount of accumulated precipitation in a given period, generally 15 minutes. Tipping bucket gauges collect rainfall in a two-chambered bucket until the weight of the precipitation causes the bucket to tip, dump the collected water and move to the other chamber under the funnel. Precipitation observations were recorded in a similar manner to the Universal Weighing and Recording gauge.

Greenways and Infrastructure

Looking west on Omaha Street, before 1972
(photo courtesy of the Rapid City Journal).

Prior to the 1972 flood, numerous homes and businesses were built along the banks of Rapid Creek. The photo on the right shows Omaha Street before the flood. The businesses located along the street were damaged or destroyed in the flood. According to statistics compiled by the United States Geological Survey (USGS) and the National Oceanic and Atmospheric Administration (NOAA), the flood caused a total of $160 million ($664 million in 2002 dollars) damage, including $37 million in residential property damage and $33 million to businesses and industries. Of the over 1,800 houses flooded, 1,335 were destroyed. Nearly 50 businesses and 5,000 cars were destroyed.

In order to prevent another flooding disaster in Rapid City, several options for hazard mitigation were discussed shortly after the flood. Several options were discussed following the flood, including the construction of a dam, a levee or straightening Rapid Creek. Straightening the channel was not well received according to the Flood Disaster Feasibility Study. The United States Army Corps of Engineers (USACE) indicated dams and levees were not considered due to sink holes. Not only would water be lost, but unstable rock formations could cause structural damage at the dam.

Looking west on Omaha Street, after the
development of the greenway (photo
courtesy of the Rapid City Journal).

The other option was to develop an open flood way along Rapid Creek. A flood way is the area of the floodplain where water is likely to be the deepest and moving the most quickly. The USACE determined which areas adjacent to Rapid Creek were in the flood way and performed channel modifications in areas where businesses could not be relocated. Within two months of the flood, officials in Rapid City began the process of acquiring property along Rapid Creek, the first step in prohibiting the construction of homes or businesses in the floodway. Approximately 750 acres of land near Rapid Creek were developed as a floodway. Over $12 million in funds from Housing and Urban Development (HUD) was allotted for relocation of homes and businesses displaced by the flood. Several sites located in the flood way were given the option of relocating, but didn't. Further expansion or development at those businesses, known as non-conforming sites, are restricted. Ordinances have been passed that prohibit development in the greenways along Rapid Creek.

One of the many bridges over Rapid Creek
destroyed in the flood (photo courtesy of the
Journey Museum).

Flood damage to roads, bridges and vehicles was estimated at $35 million (1972 dollars). When the stage, or water level, on Rapid Creek (photo at right) rose as much as 3.5 feet in 15 minutes, 15 of the 23 bridges over Rapid Creek were destroyed. Peak flow was 50,600 cubic feet per second...more than 10 times greater than the previous flood of record.

In the months following the flood, an engineering company conducted a study and determined which bridge types best withstood the flood. Debris can dam up water, worsening the effects of the flood waters. With funding from the Federal Highway Administration, the South Dakota Division of Highways and the Office of Emergency Preparedness, bridges were redesigned to prevent debris from collecting underneath. Two highway bridges were rebuilt with design consultation from the USACE.

The left bottom photo is the Canyon Lake Dam before the June 9, 1972 flood. During the 1972 flood, debris clogged the spillway at Canyon Lake, temporarily raising the pool up to 12 feet deeper than usual. The debris clog also weakened the dam, which eventually breached at 10:40 p.m. on June 9.

The first dam was constructed in 1890, but it was washed out by a flood in 1907. The lake remained dry until 1932 when the land was donated to Rapid City and the Works Projects Administration (WPA) rebuilt the lake.

The photo at the lower right is Canyon Lake shortly after the flood. Reconstruction of the lake was completed in 1976 and the spillway had been redesigned to minimize debris clogs. The lake typically holds 140 acre-feet, or enough water to cover 140 acres of land to a depth of one foot.